304 is the most common austenitic stainless: corrosion resistant, tough, and gummy. It work-hardens fast, so the golden rules are run slower, keep the tool feeding, and always take a real chip. Let the tool rub or dwell and the surface hardens into a layer that destroys edges.
Key properties
| Property | Typical value |
|---|---|
| Density | 0.289 lb/in³ (8.00 g/cm³) |
| Hardness | ~70–90 HRB |
| Tensile strength | ~85,000 psi (585 MPa) |
| Machinability | Fair (work-hardens) |
| Composition | Fe with ~18% Cr, ~8% Ni |
Cutting speeds
| Operation | HSS (SFM) | Carbide (SFM) |
|---|---|---|
| Milling | 40 – 60 | 150 – 300 |
| Turning | 50 – 70 | 200 – 350 |
| Drilling | 30 – 50 | 100 – 200 |
Convert to RPM: RPM = (SFM × 3.82) / cutter diameter. Use the Feeds & Speeds calculators.
Tooling and setup
- Tools: sharp TiAlN or AlTiN coated carbide, 4–5 flute, variable helix to fight chatter.
- Coolant: heavy flood coolant is essential to carry away heat.
- Feed: commit to a real chip load and never let the tool dwell or spin in place.
- Rigidity: minimize stickout and hold the part solidly; 304 punishes flex with chatter and work-hardening.
See Cutting Speeds for Stainless Steel and the full Feeds and Speeds Chart.